The present invention relates to a vacuum pick and place device and a pick and place confirming sensor and, more particularly, to a vacuum pick and place device and pick and place confirming sensor with which when air is sucked in from the air suction port of a pick and place nozzle by using a vacuum so as to lift a part to a vacuum cup having the air suction port, the presence or absence of the part to the vacuum cup is detected.
In general, when a small part such as an electronic component is to be transported, a vacuum pick and place device which lifts the part to an pick and place nozzle by using a vacuum is used. In a vacuum pick and place device of this type, a vacuum cup having an air suction port is formed in a pick and place nozzle. Air is sucked in from the air suction port by a vacuum generated by a vacuum generator such as an ejector or vacuum pump. Thus, the part is lifted to the vacuum cup of the pick and place nozzle.
In the vacuum pick and place device, the presence or absence of a part is determined, that is, whether or not a desired part has been lifted from a parts feeder such as a tape feeder or whether or not an lifted part has dropped while the part is transported to a parts mounting position on a printed wiring board is checked. If the part is not lifted, a process to deal with it, that is, an error process such as re-pick and place of the same part or warning must be performed at once.
Conventionally, when the presence or absence of a part lifted to a suction nozzle is to be confirmed, the pneumatic pressure in an air suction passage after the pick and place nozzle is measured by a pressure sensor. The presence or absence of an lifted part is determined on the basis of a change in pressure value measured by the pressure sensor.
This determination utilizes the following fact. When a part is lifted to the pick and place nozzle, the air suction amount from the air suction port decreases, and the pneumatic pressure in the air suction passage decreases as compared to a case wherein no part is lifted, that is, the air suction port is open.
Actually, a reference pressure indicating a pressure in the air suction passage when the air suction port is open is preset. The presence or absence of pick and place is determined on the basis of whether or not the measurement pressure value in the air suction passage actually measured by the pressure sensor during a lifting operation reaches the reference pressure value.
In the vacuum pick and place device, as the parts size decreases, the sectional area of the channel of the air suction port of the pick and place nozzle tends to decrease.
For example, in a precision electronic device such as a cell phone or electronic camera, to decrease the size and weight of the device, the area of the printed wiring board must be reduced. As a chip part such as a resistor or capacitor, a very small chip part with a size of 1.0 mm×0.5 mm or 0.6 mm×0.3 mm is used.
To lift such a part, a pick and place nozzle having a small air suction port with a channel sectional area of 0.2 mm or 0.1 mm must be used.
When, however, the channel sectional area of the air suction port of the pick and place nozzle is decreased along with the size reduction of the part, the flow rate of air passing through the small air suction port decreases. Accordingly, the difference between the reference pressure value described above and the measurement pressure value becomes very small. With the conventional scheme of detecting a pressure change with the pressure sensor, the presence or absence of a lifted part cannot be determined accurately.